The THz radiation range is usually considered between 0.3-3.0 THz. Within this range, high performance, low-cost passive and or active imaging at 0.5-1.5 terahertz (THz) has well-established benefits, but has been little explored. There is adequate radiation from terrestrial bodies at 300 K to allow passive remote sensing as well as high-resolution images of hidden objects covered under clothing or other materials. Applications include concealed weapon detection, surveillance cameras, astronomy, non-destructive material testing, as well as ample bio and medical applications. For example, THz imaging can distinguish between normal skin tissue and tumors better than both the trained eye and infrared imaging, since THz radiation penetrates a few millimeters into the skin. An example of the use of this type of radiation is described in the paper “T-Rays vs. Terrorists”, from IEEE Spectrum of July 2007 (see also: www.spectrum.ieee.org). More information on the Terahertz region may be found in Wikipedia Website, (www.wikipedia.org).
Because THz radiation is non-ionizing and its associated radiation power is low, it is also safe. Prior art FIG. 1 shows the terahertz frequency range (within 1011 to 1013 Hz 103 beyond the megahertz (106) and gigahertz (109) ranges. THz normally refers to the region of the electromagnetic spectrum between 300 gigahertz (3×1011 Hz) and 3 terahertz (3×1012 Hz), corresponding to the sub-millimeter wavelength range between 1 millimeter (high-frequency edge of the microwave band) and 100 micrometer (long-wavelength edge of far-infrared light).
The state of the art of THz imaging is summarized in reported literature. A good summary is presented by Arttu Luukanen, of VTT/mililab (www.vtt.fi/millilab). THz imaging can be classified into passive and active imaging. In passive imaging there is detection of the blackbody radiation which is emitted spontaneously by all bodies, according to their temperature and wavelength, and formulated by Planck radiation law. In active imaging, the detected body is illuminated by external sources and the reflected radiation is detected.
The two modes of imaging are compared in Table I, quoted from reporting literature on the WEB:
TABLE IPassive+Undetectable (excluding LO in heterodyne detection)+No safety concerns+Images easy to understand+No 1/r2 independence of SNR (better range)−Stringent requirements on sensitivity−Sensitive to external conditions−Favors focal plane array architectures (expensive!)Active+Relaxed requirements on sensitivity+Favors scanning architectures+Cheaper−Limited range (SNR ∞r2)−Detectable−Harder image interpretation−Angle diversity for short ranges only−Safety concerns−Issues with irradiating non-cooperative subjects/covert surveillance
Passive imaging offers considerable advantages compared to active imaging. Passive imaging is undetectable and offers covert surveillance, does not introduce safety concerns, offers better range, does not require multiple and expensive THz sources, images are easier to interpret and favors focal plane array architectures.
The state of the art of available technologies for THz imaging is summarized in Table II, quoted from reported literature on the WEB:
TABLE IIsummary of state of the art available technologies for Thz imaging.TechnologySensitivityCostPerformanceCoherent HeterodynegoodHuge>1THzCoherent direct (with MMICgoodLarge~200GHzpreamplification)Cryogenic MicrobolometersgoodLarge>1THzIncoherent directModerate toSmall600GHz(with no amplification)goodUncooled Antenna CoupledPoor (activeLow>1THzMicrobolometersonly)Plasma transistorsModerateLow~1THzThe present inventionHighLow>1THzSource: Microsensor seminar, presented by Arttu Luukanen, www.vtt.fi/millilab.
According to Table II, low cost imaging should be based on antenna coupled bolometers but the state-of-the-art sensitivity is poor and hence only active imaging is possible. Cryogenic microbolometers (based on superconductors) may provide good sensitivity but the required temperature of operation is 10K or lower, thus increasing considerably the system cost. Coherent detection using MMIC pre-amplification is limited to ˜200 GHz. This technology offers good sensitivity but system cost is large. Coherent heterodyne detection may be applied to THz radiation, with good sensitivity but at huge cost.
It is seen that low cost performance, based on current approaches of Antenna Coupled Micro Bolometers (ACMB) is limited only to Active Imaging Systems. ACMB performance is typically Noise Equivalent Power (NEP) ˜50-100 pWatt/Hz1/2 and pixel count is limited by real estate (since pixel dimension should be of the order of the wavelength and is therefore 600 microns for 0.5 THz radiation).
Thermal sensors and the FPA are well-explained in the first reference below, (U.S. Pat. No. 7,489,024), by at least one of the inventors of the current invention, and is incorporated herein by said reference.
This and other prior art references are contained in the following list of publications:    1. E. Socher, O. Degani and Y. Nemirovsky, “TMOS-Infrared uncooled sensor and focal plane array”, U.S. Pat. No. 7,489,024, issued Feb. 10, 2009.    2. E. Socher, S. M. Beer and Y. Nemirovsky, “Temperature Sensitivity of SOI-CMOS Transistors for Use in Uncooled Thermal Sensing”, IEEE Trans. Electron Devices, Vol. 52, no. 12, pp. 2784-2790, December 2005.    3. L. Gitelman, S. Stolyarova, S. Bar-Lev, Z. Gutman, Y. Ochana, and Y. Nemirovsky, “CMOS-SOI-MEMS transistor for uncooled IR Imaging”, IEEE Trans. Electron Devices”, Vol. 56(9), pp. 1935-1042, September 2009.    4. L. Gitelman, Z. Gutman, S. Bar-Lev, S. Stolyarova and Y. Nemirovsky, “CMOS-SOI-MEMS Transistor for Infrared Imaging”, IEEE/LEOS International conference on Optical MEMS & Nanophotonics, Freiburg, Germany, August 2008. ISBN: 978-1-4244-1917-3    5. L. Gitelman, Z. Gutman, S. Bar-Lev, S. Stolyarova and Y. Nemirovsky, “TMOS Novel Uncooled Sensors—Theory and Practice”, IEEE COMCAS 2008, The International IEEE Condference on Microwaves, Communications, Antennas and Electronic Systems”, Tel Aviv, Israel, May 13-14, 2008. ISBN: 978-1-4244-2097-1    6. E. Socher (Ph.D thesis performed at Technion-Israel Institute of Technology.), “CMOS Infrared Imagers”, (1999-2005). (supervised by Y. Nemirovsky).    7. L. Gitelman (M.Sc thesis performed at Technion-lsrael Institute of Technology.), “Study of micromachined transistors as uncooled sensors for IR imaging”, (2004-2006) (supervised by Y. Nemirovsky).    8. Zivit Gutman (M.Sc.), “Study of CMOS-SOI-MEMS transistors and systems”, (2006—thesis performed at Technion-Israel Institute of Technology). (supervised by Y. Nemirovsky).